Hard drive full but doesnt look to be

hi ok i got 111Gb hard drive and my program files say filled up 30gb so that would be all my games then windows is 9gb and there is a folder thats 1.2gb and in users 17gb and thats all I have used and It reckons that I only have 9gb left. I dont know whats going.
any suggestions what I should do I really dont want to format though.
thanks

how about restore partition make of machine
OEM 's like to put a restore section hidden on system this way they don't have to give you a OS disc
on the subject you may have to many restore points
or page file gone nuts

Thats what I was referring to,checking to see that trhe drive isnt having any problems by scanning it mitcho4.
Samstoned brings up a good point as the system restore space could be quite large on top of any oem info being stored.